(a) Field of the Invention
The present invention relates to a method for vapor deposition of a metal compound film in a semiconductor device and, more particularly, to a method for deposition of a metal oxide or metal nitride film by depositing monoatomic layers thereof one on another in a semiconductor device.
(b) Description of the Related Art
Along with the recent development of higher integration of LSIs, it is an important subject on the fabrication of LSIs to form a variety of thin films with excellent reliability and uniformity on a silicon wafer. In particular, it is desired that the gate insulating film underlying the gate electrode of a MOSFET have lower leakage current, higher withstand voltage, higher reliability, and uniformity of film thickness. Dielectric films made of SiO2-based material are generally used as the gate insulating films heretofore, and are formed by a thermal oxidation process. On top of the gate insulating film, a polysilicon electrode is generally formed as the gate electrode by using a low pressure CVD (LPCVD) technique.
In the circumstances as described above, the gate insulating film has a thickness as small as 2 nm or less in consideration of the scaling rule of the up-to-date MOSFETs. Such a small thickness of the gate insulating film involves a problem of increase in the gate leakage current. For solving this problem, introduction of metal oxide dielectric films having a higher dielectric constant than the SiO2 film is actively studied. This is considered because the effective film thickness in terms of the thickness of SiO2 film having a dielectric constant of 4.0 can be reduced for an insulating film, if the insulating film has a higher dielectric constant, to obtain an equal insulating capability for suppressing the leakage current.
The metal compound dielectric film should be thermodynamically stable in relation to silicon, and thus introduction of Al2O3, ZrO2, HfO2, lanthanide oxides etc. is considered (refer to, for example, “IEDM Technical Digests 2000”, 653 pp by H. J. Osten). Among others, an Al2O3 film is generally expected as an excellent dielectric film for replacing the SiO2 film because the Al2O3 film has been used heretofore as an insulating film. However, the dielectric constant of Al2O3 is moderate and resides around 10.0. Thus, materials having higher-dielectric constants such as ZrO2 having a dielectric constant of 25, a HfO2 having a dielectric constant of 30 and lanthanide materials are studied for forming the next-generation insulating films. In alternatives, an aluminate film, wherein Al2O3 film is added with zirconium (Zr) or hafnium (Hf), and a silicate film, wherein SiO2 film is added with Zr or Hf, are also expected as the next-generation insulating films (refer to, for example, “IEDM Technical Digests 2000”, 23 pp, by L. Manchanda).
On the other hand, in deposition of a gate insulating film, it is especially important to assure the in-plane uniformity of the film thickness within the wafer. For example, the in-plane uniformity of the film thickness is required to reside within ±5 nm in the case of forming a gate insulating film having a thickness of 1.5 nm in terms of the SiO2 thickness.
In the deposition of the higher-dielectric-constant gate insulating films, among a variety of conventional processes such as reactive sputtering, thermal oxidation treatment after metal sputtering, and CVD (chemical vapor deposition), an atomic layer deposition (ALD) technique has attracted large attention due to the excellent in-plane uniformity of the film thickness within the wafer. The ALD technique is such that metal oxide is vapor-deposited by stacking monoatomic layers thereof one on another. For deposition of the metal oxide film by using the ALD technique, alternate irradiation of trimethylaluminum (TMA) and water is used in the case of Al2O3, and alternate irradiation of a chloride material and water is used in the case of ZrO2 or HfO2.
In the conventional ATM technique for deposition of ZrO2 or HfO2, there is a problem in that the chloride used as the source gas remains in the resultant film. The residual chloride remaining in the deposited film degrades the reliability of the semiconductor device during the succeeding processes. In the case of an aluminate film or a silicate film including Zr or Hf, a chloride is also used as the source material, which involves a similar problem. In the case of introduction of lanthanide materials, the chloride used as the source material is solid and it is difficult to deposit this source material by using a vapor deposition technique.